Evolution / Genetics / Biology

Largest Ichthyosaurus was pregnant mother

Scientists from the UK and Germany have discovered the largest Ichthyosaurus on record and found it was pregnant at the time of death.

Life reconstruction [Credit: University of Manchester]

The new specimen is estimated to be between 3 and 3.5 m long and is an adult female. Ichthyosaurs were a highly successful group of sea-going reptiles that became extinct about 90 million years ago. Often misidentified as swimming dinosaurs, these reptiles appeared before the first dinosaurs had evolved. The largest species of ichthyosaur grew to over 20 m in length.

The new specimen was originally discovered on the Somerset coast, during the mid-1990s, and is from the Early Jurassic, roughly 200 million years old. However, the specimen remained unstudied until it wound up in the collections of the Lower Saxony State Museum in Hannover, Germany.

Palaeontologist Sven Sachs of the Bielefeld Natural History Museum (Germany) first saw the specimen in August 2016, whilst on a routine visit. He informed University of Manchester palaeontologist and ichthyosaur expert, Dean Lomax, and together, the pair examined the new specimen in early 2017. They identified it as an example of an Ichthyosaurus somersetensis, a new species that Dean and another colleague, Prof. Judy Massare, had previously identified.

Skeleton of Ichthyosaurus [Credit: Dean R. Lomax]

Dean said "It amazes me that specimens such as this [the biggest] can still be 'rediscovered' in museum collections. You don't necessarily have to go out in the field to make a new discovery. This specimen provides new insights into the size range of the species, but also records only the third example of an Ichthyosaurus known with an embryo. That's special"

The embryo is incomplete and preserves only a portion of the back bone, a forefin, ribs and a few other bones. The preserved string of vertebrae is less than 7 cm long. The bones of the embryo are not fully ossified, meaning that the embryo was still developing.

Another intriguing discovery the duo made was that the tail of this new specimen did not belong with the rest of the skeleton. A tail from another ichthyosaur had been added to the skeleton to make it appear more complete and visually appealing for display.

Dean Lomax & Sven Sachs [Credit: University of Manchester]

Sven added "It is often important to examine fossils with a very critical eye. Sometimes, as in this instance, specimens aren't exactly what they appear to be. However, it was not 'put together' to represent a fake, but simply for a better display specimen. But, if 'fake' portions remain undetected then scientists can fall foul to this, which results in false information presented in the published record.

"Specimens like this provide palaeontologists with important information about when these animals lived. Many examples of Ichthyosaurus are from historical collections and most do not have good geographical or geological records, but this specimen has it all. It may help to date other ichthyosaur fossils that currently have no information."

Ichthyosaurus is one of the most common fossil reptiles in the UK, with thousands of specimens known, ranging from isolated bones to complete skeletons. Some of the very first examples were collected from along the Dorset coast by Victorian palaeontologist, Mary Anning, who first brought them to the attention of the scientific world.